Medical diagnosis that utilizes ultrasound imaging has recently been widely used in medical fields. The ultrasonic image is obtained by emitting ultrasound from an ultrasonic probe toward a necessary body part and detecting echo from the body part as electric echo signals by use of an ultrasound observing device that is connected to the ultrasonic probe through a connector. The ultrasonic probes may be classified roughly into an intra-cavity diagnostic type that is inserted in a body cavity, and an extra-cavity diagnostic type that is moved on the body surface. As a known driving methods for the intra-cavity diagnostic ultrasonic probe, there is an electronic scanning method, wherein a plurality of ultrasonic transducers are selectively driven to send and receive the ultrasound, while being switched over by electronic switches or the like.
The electronic scanning type ultrasonic probes may be classified into a convex electronic scanning type and a radial electronic scanning type. In the convex electronic scanning type, the ultrasonic transducers, e.g. 94 to 128 transducers, are arranged on a semi-cylindrical surface of a probe tip. In the radial electronic scanning type, the ultrasonic transducers, e.g. 360, are arranged around a periphery of a probe tip.
In those types of ultrasonic probes using a plurality of ultrasonic transducers, such as the convex electronic scanning type and the radial electronic scanning type, it is necessary to provide wiring cables for sending and receiving many kinds of signals, including drive signals for exciting the individual transducers and the echo signals, between the ultrasound observing device and an electric circuit disposed in the ultrasonic probe. Therefore, the cables take up a certain thickness in the ultrasonic probe, and hinder making the ultrasonic probe finer, although it is desirable to make the intra-cavity type probe as fine as possible in order to ease the pain of the patient.
Since the available number of ultrasonic transducers to one probe is limited by the permissible thickness of the wiring cable, the resolving power of the ultrasonic image has also been limited. Beside that, if the wiring cable has a large capacitance, the echo signal will damp. Mismatching of electric impedance will lower the S/N ratio, and may also cause cross-talk between the wires, which can result in malfunction.
To solve the above problems, U.S. Pat. No. 4,917,097 suggests an ultrasonic transducer device wherein ultrasonic transducers are integrated with amplifies for the echo signals without using a wiring cable, and Japanese Laid-open Patent Application No. 2000-298119 suggests an ultrasonic transducer device wherein an electric circuit is mounted on a silicon substrate that is integrated with ultrasonic transducers made of composite piezoelectric elements, so as to make the wiring cables unnecessary for connecting the electric circuit and the ultrasonic transducers.
Recently, an ultrasonic transducer device using capacitive micromachined ultrasonic transducers, which utilize micro electromechanical system (MEMS), has been suggested, for example, in U.S. Pat. No. 6,246,158 and Oralken et al, “Volmetric Ultrasound Imaging Using 2-D CMUT Arrays”, November 2003, IEEE TRANSACTION ON ULTRASONIC, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 50, NO. 11.
However, according to the prior arts disclosed in the above first and second materials, the amplifiers and the electric circuit are arranged in a lateral direction of the ultrasonic transducer. In that case, if the ultrasonic transducers are arranged to set their lateral direction in alignment with an inserting direction of the ultrasonic probe, the ultrasonic probe will have a relatively large hard portion including the ultrasonic transducers, increasing the load on the patient that may be caused by inserting the ultrasonic probe into the living body.
Furthermore, since the first and second prior arts refer to an example where the ultrasonic transducers are arranged in a linear array, if the amplifiers and the electric circuit are arranged laterally to the ultrasonic transducers, the wiring between these elements and the ultrasonic transducers will be complicated.
On the other hand, in the ultrasonic transducer device of the first prior art, U.S. Pat. No. 6,246,158, an electric circuit is disposed as a layer under the ultrasonic transducers. However, there is no concrete description about how to connect the electric circuit to wiring cables, how to arrange the ultrasonic transducers or how many ultrasonic transducers are available. Among all, there are not any suitable embodiments for the convex electronic scanning type or the radial electronic scanning type.